1. Field of the Invention
This invention relates to a control system for mechanical presses, and, more particularly, to an automatic control system for adjusting the counterbalance for such a press.
2. Description of the Prior Art
Mechanical presses are commonly used for stamping, bending, blanking, embossing and otherwise shaping materials, usually metals. Replaceable die sets are used to do such forming with a lower die half attached to a stationery bed or platen and an upper die half attached to a ram or slide which reciprocates vertically. Typically in a mechanical press, an electric motor is used to rotate a counterweight or flywheel, bringing the rotational speed of the counterweight up to a no-load equilibrium speed which will provide the proper kinetic energy to perform the forming operation. A clutch mechanism engages the flywheel which, through gears and mechanical linkage, reciprocates the ram in its working cycle using the inertia of the flywheel. Counterbalances are used to counterbalance the moving weight of the ram and its attached upper die half or punch to provide smooth operation, easier stopping, and less wear on the gears, bearings and other moving parts of the press.
Mechanical presses commonly use one or more pneumatic cylinders to perform the counterbalancing function. Typically, the air pressure is adjusted by the press operator through a manual pressure regulator when a new set of dies are put into the press to compensate for the change in the weight of the die. Usually, very little further adjustments are made of the air pressure, unless they are made pursuant to the "feel" that an experienced operator has in the efficient running of the press.
Systems have been developed for automatically adjusting the air pressure in an attempt to compensate for various effects. For example, in U.S. Pat. No. 4,283,929, the die sets, or at least the upper die or punch member is encoded so that when a new die set is put into the machine, this coding is read by the machine to automatically make an adjustment in the counterbalance air pressure to compensate for the change in the weight of the die. Other attempts have been made to automatically compensate for change in the die weight and the speed of the press by measurement of the motor current only. U.S. Pat. No. 4,069,697 teaches changing the air pressure responsive to a current signal so that adjustment for excess counterbalancing is accomplished on a down stroke and compensation for insufficient counterbalancing is done on an upstroke. Unfortunately, adjustments for die weight or motor current only solves part of the problem.